Exemplary embodiments of the present invention relate to an electrostatic discharge (ESD) protection circuit for use in a semiconductor circuit, and more particularly, to a circuit configuration which is capable of preventing malfunction of a multi-finger transistor used in an ESD protection circuit.
When a semiconductor integrated circuit (IC) comes in contact with a charged human body or machine, static electricity charged in the human body or machine may be discharged to internal semiconductor circuits through external pins and input/output pads of the semiconductor IC. At this time, a transient current with high energy may cause severe damage to the internal semiconductor circuits. In some cases, static electricity charged in the inside of the semiconductor circuits may flow through the machine, due to the contact with the machine, and cause damage to the machine.
In order to protect internal semiconductor circuits from such damage, most semiconductor ICs are provided with an ESD protection circuit coupled between an input/output pad and an internal semiconductor circuit.
FIG. 1 illustrates a typical ESD protection circuit that includes a multi-finger transistor.
Referring to FIG. 1, the conventional ESD protection circuit includes an input/output pad 100, a voltage pad 102, a voltage line 104, a plurality of first finger patterns 110, 112, 114 and 116 corresponding to a plurality of drains, a plurality of second finger patterns 120, 122, 124, 126 and 128 corresponding to a plurality of sources, and a plurality of gate electrodes 130, 131, 132, 133, 134, 135, 136 and 137.
In the conventional multi-finger transistor of FIG. 1, the first finger patterns 110, 112, 114 and 116 corresponding to the drains, and the second finger patterns 120, 122, 124, 126 and 128 corresponding to the sources are alternately arranged in parallel.
The gate electrodes 130, 131, 132, 133, 134, 135, 136 and 137 are arranged between the first finger patterns 110, 112, 114 and 116 and the second finger patterns 120, 122, 124, 126 and 128, respectively.
The drains are coupled to the input/output pad 100 through the first finger patterns 110, 112, 114 and 116, which are coupled to a plurality of first contact patterns (shown in FIG. 1 as a plurality of small squares in each of the first finger patterns 110, 112, 114 and 116). The sources are coupled to the specific voltage line 104 through a path, which includes the second finger patterns 120, 122, 124, 126 and 128 and the voltage pad 102, through a plurality of second contact patterns (shown in FIG. 1 as a plurality of small squares in each of the second finger patterns 120, 122, 124, 126 and 128). The gate electrodes 130, 131, 132, 133, 134, 135, 136 and 137 are coupled to the voltage line 104 through the sources and the voltage pad 102.
When positive static electricity is applied to the input/output pad 100, an ESD path R1 is formed from the first finger pattern 110, corresponding to the drain, through the second finger pattern 120, corresponding to the source, to the voltage line 104. An ESD path R4 is formed from the first finger pattern 116, corresponding to the drain, through the second finger pattern 126, corresponding to the source, to the voltage line 104.
Although only two ESD paths R1 and R4 are illustrated in FIG. 1, more ESD paths may be formed according to the number of the finger patterns.
In the multi-finger transistor, the ESD paths are formed by the respective finger patterns between the input/output pad 100 and the voltage line 104. Since a normal current (IT2), that the finger patterns can endure without malfunctioning, is already determined in a design step, the multi-finger transistor may malfunction when an ESD current more than the normal current (IT2) is transmitted through the finger patterns.
The ESD path R1 is the shortest ESD path because it is closest to the voltage line 104. Thus, the ESD path R1 has the lowest resistance. On the other hand, the ESD path R4 is the longest ESD path because it is farthest from the voltage line 104. Hence, the ESD path R4 has the highest resistance.
Therefore, most of the ESD current is transmitted through the ESD path R1 with the lowest resistance instead of through the ESD path R4 with the highest resistance. Consequently, a different amount of ESD current is transmitted through the respective ESD paths. In other words, among the ESD paths, the largest amount of ESD current is transmitted through the ESD path R1.
If an excessive amount of ESD current is transmitted through the ESD path R1, and this ESD current is larger than the normal current (IT2), the contact patterns of the finger patterns forming the ESD path R1 may be melted, causing malfunction of the multi-finger transistor.
Even though the malfunction occurs in any one of the finger patterns, the entire ESD protection circuit cannot be used any more. Therefore, as described above, if the malfunction is caused by the melting of a contact pattern of a specific finger pattern, the entire multi-finger transistor does not properly operate as the ESD protection circuit.
One of methods for preventing such a malfunction is to increase the size of a unit finger pattern of the multi-finger transistor to increase an amount of transmitted ESD current the respective finger patterns can endure. In this case, however, the layout area of the multi-finger transistor increases, which is a concern in fabricating highly integrated semiconductor devices.